Is Your Strength-Training Routine Messing with Your Runs?

My first marathon sucked. My knee hurt so bad that—instead of cheering—spectators started asking me if I was okay: I made eye contact, shook my head “no,” and kept running. This must look really bad, I thought.

It certainly felt bad. My knee had been acting up all training cycle—and it started hurting around mile 5. I spent the next 9 miles bracing myself for the worst, then the following 12 miles mastering a strategy that involved using my right hip to drive my right leg forward in a limping motion. I finished in 05:14. Honestly, I’m shocked it didn’t take longer.

I’m equally shocked that I caught the marathon bug after that—but I was determined to run an injury-free race next time. I went to yoga, I tried barre, I doubled down on weight lifting. I already lifted every other day, but hey, maybe I needed to try harder.

“Trying” wasn’t the issue, because my next training cycle was worse. Tendonitis—as I later learned from my physical therapist—made yet another marathon miserable, and I finished my second 26.2-mile race 10 minutes slower than my first—a PR in the wrong direction.

It seemed that no matter how hard I tried, I always found myself in physical therapy, committing to a life of clam shells and Pilates, on the verge of pulling out of an upcoming marathon. I wondered if distance running just wasn’t for me, but I also started to become skeptical of my lifting strategy. So, as an experiment, I completely stopped hitting the weight room while training for the Los Angeles Marathon.

The result: I took a full hour off of my time (!) and crossed the finish-line feeling, well, strong. My first injury-free marathon was in the books—and oh, it felt good. Real good.

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But I called up James Bagley, Ph.D., an assistant professor of kinesiology at San Francisco State University, to see where I went wrong. “You did what a lot of people do—over train,” he says. “Lifting should reduce your risk of injury if you’re doing it right.”

He’s definitely right about the overtraining part: I was lifting heavy about four times a week—and I’d leave the weight room feeling worked. “By the time you’re in marathon-training mode, you should never be sore from lifting,” Bagley says. Yep, I was often sore.

Lifting too hard is problematic for runners because it means you’re probably not recovering properly, Bagley says. And recovery is important: a Sports Medicine review concluded that resistance training can impair endurance performance if you don’t recover in between workouts, which can take longer than you think.

Plus, Bagley says your muscles and neurons adapt to strength training much faster than your tendons do, which can be a recipe for tendonitis. “Repetitive movements, like running or lifting a lot of repetitions of the same exercise, cause microscopic tears to muscle and tendons,” he says. “Muscles can repair these tears quickly to build more muscle, but tendons take longer to recover, causing inflammation.”

So much for trying harder, right?

Of course, this doesn’t mean you should stop lifting altogether. I slowly started incorporating strength training back into my routine, and I took another 15 minutes off my time the following year. And it’s worth noting that I had already built up quite a bit of strength in advance of the Los Angeles Marathon—I just stopped during the training cycle to avoid the overtraining issue.

Ignore your body-builder friend.

Bagley explains that you want to gain strength without gaining muscle mass, which means you need to lift heavier weight (80 percent of your one-rep max) at lower reps (three to five reps is plenty), instead of the traditional 10 to 12 reps at 60 to 80 percent of your one-rep max. The latter is the classic bodybuilding model, Bagley says, but “runners don’t need to be big, they need to be strong.”

Your strength workout should feel nothing like cardio.

“You don’t need to lift for endurance (again, go for heavy weights and low reps), because you’re already training your endurance when you’re running,” Bagley says. Take two to three minutes of rest in between sets, and make sure you aren’t dying at the last rep.

Kiera CarterKiera Carter has a decade's worth of experience covering fitness, health, and lifestyle topics for national magazines and websites.

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